In a 3 hour time frame most bases attacked would be griefed to shit, I like the idea but it doesn't work as it'll be more of a mass shitfest than rewarding PvP. I'd love some kind of weekly PvP event, and when this would promote raiding it would also become the center of PvP, it'll revolve around this, after a while it'd become more of a chore.
What'd be better is something like a weekly hunt. Admins could create an unclaimable base somewhere (Like a warzone but with block placement and breaking allowed), it'll have some traps, chests full of loot and other stuff. The general coords could be released and people who are online can go to raid the house. This will require a few people being online. Anyway, people will have to find the exact coords of the base and help their faction/allies to get there, once the base has been found, admins should then release the Coords publicly, so the faction that has got into the base must now dodge the traps, find the goods and defend the base until they're done, everything will be allowed. The base will not be deleted, after a day the base will be claimable.
This is just a quick example of some weekly event that could be done instead, there are loads of things that could get people more involved in PvP, not even weekly, constantly. I understand your reasoning and idea, but I'm not too sure.